This invention relates to a mechanical seal.
When a sealing liquid is a slurry liquid such as a pulp slurry or the like solid materials invade into a sealing face clog into a spring or the like, and various troubles are caused, such as imperfect sealing due to abrasions in the sealing face or unsatisfactory sliding of a slide ring.
Therefore, the prior art has devised to supply a clean liquid from the outside, or to provide a souble mechanical seal.
Using the prior technique of supplying clean liquid from the outside, the above-mentioned defects are removed. However, a new problem arises in that the sealing liquid is diluted. On the other hand, when the amount of supplied clean liquid is decreased to avoid said dilution of the sealing liquid, those defects as above mentioned cannot be solved satisfactorily.
Although the double mechanical seal does not involve a problem of dilution of the sealing liquid, the structure thereof is complicated and increases cost of the apparatus.